The sophistication and overall quality of audio cables has progressed rapidly over the past several years and now stands as a dominant specialty of serious audio technology. A perfect audio interconnection cable has, in one sense, become the holy grail of the high end audio field. As other audio components such as amplifiers, preamplifiers, CD players, speakers, etc. have rapidly evolved, they have continued to be interconnected by cables with similar, and in some cases identical, geometries to their 1940's era ancestors. Many entrepreneurs have leapt into the gulf in an attempt to both improve the quality of sound as well as to capitalize on this booming market.
Typically, an audio system consists of: an audio signal source (e.g., a turntable, FM tuner, CD player, microphone, tape deck, etc); an amplifier, either integrated or consisting of a separate pre-amplifier and power amplifier; and finally speaker (i.e., a loudspeaker) system. All these devices must be interconnected by suitable electrical cables, heretofore usually of different types depending on the nature of electrical signals to be carried. Even if the component interconnections are theoretically simple, experience shows that the interconnection cables may greatly influence the quality of the signal reproduced by the audio system. The interconnection cables are known to influence at least: the tone-color of the signal; the spatial reconstruction of the audio “image”; the amount of lost information; the focusing of the sound sources; the dynamic range; the audibility of the sound event; the naturalness of the reproduced sound, and the noise level introduced into the audio signal. These, as well as other variations and distortions imposed on an audio signal by an interconnect cables are all degradations of the reproduced signal with respect to the original event.
Although the impact of an audio interconnection cables on the overall quality of an audio system has been recognized since the inception of electronic high-fidelity equipment, the development of specialized audio cable for serious high-fidelity applications begin in the 1970's. Pioneered by Robert Fulton, early audiophile cables improved sound quality by focusing primarily on the materials used in the cable. The use of copper as a conductor as well as the use of stranded conductors are examples of such developments. Concentric conductor (i.e., coaxial) cables have long been used for transmission of audio signals. Coaxial cables that include dielectric washers made of rubber or glass between the concentric conductors have been proposed, for example, as disclosed in U.S. Pat. No. 1,818,027 issued to Affel, et al. Helical polymer spacers have been used between olefin polymers to separate conductive layers as taught in U.S. Pat. No. 3,309,455 to Mildner. Fulton was one of the first to address the issue of frequency dependent signal timing by developing cable of specific lengths. Signal timing considerations were further addressed by Brisson (U.S. Pat. No. 4,538,023) and Magnan (U.S. Pat. No. 4,767,890). Different sized conductors within a single cable have also been proposed as in U.S. Pat. No. 4,628,151 to Cardas.
The aforementioned, as well as other specialized cables have made progress towards an optimum cable that, theoretically, introduces no degradation into an audio or other signal being conducted by the cable. Heretofore, however, these attempts have meet with only limited success. While some cables of the prior art have overcome a few of the known problems, they have not yet reached a point of becoming “acoustically invisible”. The present invention, however, provides cables which move considerably closer to acoustic invisibility than any cable of the prior art. While prior art cables have been constructed differently depending upon their function (i.e., their placement in the overall audio signal path), the cables of the present invention use identical geometries regardless of their function. For example, the same cable geometry may be used for a cable from a moving coil phono cartridge carrying a signal in the low millivolt range as for a power cable carrying several amps of line current to a power amplifier. The same cable geometry is used regardless of whether the carried signal is analog or digital, audio or video, or even AC power. It has even been hypothesized that a high-voltage automobile ignition cable might benefit from a construction in accordance with the present invention.
Evaluating an audio cable's performance is not an easy task. Fortunately, the human ear is a remarkable, wide-range transducer whose dynamic range is estimated to be on the order of 140 dB. This is a far greater dynamic range than is often obtainable in typical electronic circuits and test equipment. Because the ear is so sensitive that small, often otherwise unmeasurable, changes or distortions in an audio signal are audible to and detectable by a discerning ear. There is an old adage, if something sounds good, it will measure “good”. However, not everything that measures “good” will sound good. Because, at least for audio interconnection cables, the ultimate “consumer” is the human ear, such ears have been enlisted to evaluate the cables of both the prior art and the present invention. Two cables may both measure well using conventional, generally accepted standards of impedance, capacitance, inductance, noise, etc. However, those two cables with seemingly identical measured electrical characteristics may not sound the same to the trained ear, for example, when listening to music.